Atty. Mark C. Nielsen
Mark’s background includes a broad array of multijurisdictional and complex commercial disputes, including class action litigation. He has practiced before state and federal courts, as well as in arbitration actions, and he has been involved in all aspects of litigation—from pretrial discovery and motion practice to trial advocacy and appellate practice.
Profile Summary
About Mark C. Nielsen at a glance
Mark C. Nielsen is a employment and litigation attorney based in Washington, District of Columbia, practicing at Groom Law Group Chartered. Educated at New York University (J.D., 1997). Recognitions include Best Lawyers in America — Litigation - ERISA (2026), Best Lawyers in America — Additional Areas of Practice: (2026), and Best Lawyers in America — Employee Benefits (ERISA) Law (2026). Serands clients in Washington, DC and the surrounding metropolitan area.
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About
- Mark’s background includes a broad array of multijurisdictional and complex commercial disputes, including class action litigation
- He has practiced before state and federal courts, as well as in arbitration actions, and he has been involved in all aspects of litigation—from pretrial discovery and motion practice to trial advocacy and appellate practice
- He regularly represents plans, their sponsors, and insurance companies before federal and state regulatory agencies
- As a litigator, he has successfully defended plan trustees and plan sponsors in federal court against breach of fiduciary duty and prohibited transaction claims brought by the Department of Labor and plan participants and beneficiaries
- These claims involved complex commercial real estate developments, stock option and stock repurchase programs, and multiple employer welfare arrangements
- He has also successfully defended plans and their fiduciaries in benefit claim disputes in both trial and appellate courts, and he has successfully defended employers against claims arising under the Americans with Disability Act
- In addition, Mark regularly counsels plans, plan trustees, and plan sponsors as to their fiduciary obligations under ERISA
- These include duties attendant to plan investments and transactions, as well as the requirements of federal and state health care laws, including Medicare Part D, HIPAA, COBRA, and the Age Discrimination in Employment Act
- Mark previously served as a member of the firm’s Executive Committee
Practice Areas Explained
Mark C. Nielsen's Areas of Practice
Each practice area below reflects the types of cases Mark C. Nielsen handles, with a brief overview of what that area of law covers.
Employment lawyers represent workers in wrongful termination, discrimination, harassment, wage & hour disputes, and severance negotiations.
Mark C. Nielsen is one of 169,120 employment attorneys indexed nationally. Browse employment attorneys in District of Columbia →
Civil litigation attorneys for breach of contract, business disputes, civil rights, and class action lawsuits.
Mark C. Nielsen is one of 454,532 litigation attorneys indexed nationally. Browse litigation attorneys in District of Columbia →
Jurisdictional Context
Why local counsel matters in District of Columbia
Practicing law in District of Columbia. Legal matters in District of Columbia are governed by state-specific rules of civil and criminal procedure, statutes of limitations, and substantive law. Cases originating in Washington are typically filed in the local municipal court or the appropriate District of Columbia state district court, depending on subject matter and amount in controversy. An attorney licensed in District of Columbia brings working knowledge of local procedural deadlines, judicial practices in this andnue, and the substantive law that applies to cases brought here. Out-of-state attorneys generally cannot represent clients in District of Columbia courts without local counsel or pro hac vice admission.
Looking for additional District of Columbia attorneys? Browse all attorneys in Washington or all attorneys in District of Columbia.
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